problem with sharp transitions between rotation keyframes
The Gimbal Lock ... maybe?

You might have tripped on "Gimbal Lock" problem with Euler. And yes Quaternions method let you avoid the "Gimbal Lock" issue. There is a very clear video about gimbal lock issue here ... 

https://www.youtube.com/watch?v=zc8b2Jo7mno&amp;list=PLLJePYWucKoOm0NN3blOFqAlvL5Etyf6A

Understanding the topic may help you avoid gimbal lock if you want to continue
using Euler solutions. To summarise what I have learn is that if your object is a camera, you can avoid Euler's gimbal lock with some good knowledge and learn how to avoid them. However if you are working of an object like a fighter jet that has radical rotation in your scene, it's best to apply Quaternions.